Modern optical systems should meet ever more stringent requirements in respect of image quality. The important aberrations, which should be kept low by the configuration of the optical system, include e.g. field curvature and astigmatism. In the case of field curvature, the image arises in a different plane along the optical axis depending on the field point. Thus, a field-dependent defocusing aberration emerges for planar image fields, for example a camera chip.
Highly precise and high-quality optical units may be used to reduce such aberrations. This often leads to complicated, large and expensive optical systems. Moreover, a large number of lenses may increase the reflection susceptibility of the system and/or reduce the transmission. This may be disadvantageous for many applications, for example in the field of expensive specialist appliances.
Alternatively, or additionally, use may be made of image sensors with curved image sensor surfaces at least in specialist applications for field curvature correction. However, this is not always possible and leads to increased costs. A further option for reducing the defocusing aberration caused by the field curvature consists of the use of optical systems, the overall depth-of-field of which is greater than the object field curvature. However, the numerical aperture of the overall system needs to be reduced to this end, leading to losses in resolution.
Alternatively, use may be made of more cost-effective optical units in combination with subsequent post-processing. Apparatuses and methods which combine cheaper optical units with subsequent post-processing may contain deconvolution techniques in the digital further processing. Such techniques, for example iterative deconvolution techniques, are often associated with high computational outlay. This may be found to be disadvantageous, in particular, if a fast calculation of an image is desired, for example for the real-time display of recorded specimen regions in a microscope system. Direct deconvolution methods may suffer from low accuracy and have a restricted field of application. A low contrast of the modulation transfer function (MTF) and/or a poor signal-to-noise ratio (SNR) of the image may lead to certain spatial frequencies determined using deconvolution techniques not being reconstructable or only being reconstructable under certain additional assumptions. By way of example, this may be the case for spatial frequency regions in which, on account of aberrations, the MTF has zeros. By way of example, such zeros in the MTF may occur in the case of astigmatism or defocus. Longitudinal chromatic aberrations may not be easily compensable by means of deconvolution techniques.